A hydraulic jar is a mechanical tool employed in downhole applications to dislodge drilling or production equipment that has become stuck within a wellbore. Typically, the hydraulic jar is positioned in the drill string as part of the bottom hole assembly (BHA) and remains in place throughout the normal course of drilling operations.
As the name hydraulic “jar” implies, the function of this tool is to provide a jarring impact to free the drill bit, or another portion of the drill string, should it become stuck. A drilling jar generally consists of a first tubular member, typically referred to as a housing, which telescopically receives a second tubular member, typically referred to as a mandrel. The second tubular member is capable of limited axial movement within the first tubular member, referred to as a stroke. The first tubular member has an impact surface referred to as an anvil. The second tubular member has an impact surface referred to as a hammer. At the end of each stroke, the hammer and anvil are brought into a sudden and/or forceful contact to free the wedged drill bit.
A typical hydraulic jar includes the mandrel slidably disposed within the housing with a central bore therethrough. During drilling operations, a fluid, e.g., drilling mud, is delivered through the central bore to the drill bit. The upper end of mandrel is coupled to the drill pipe, while the lower end of mandrel is slidably received within housing. The lower end of housing is coupled to the remaining components of the BHA. A sealed annular chamber, containing hydraulic fluid, is disposed between mandrel and the housing. A flow restrictor is disposed within the chamber and coupled to the mandrel, separating the chamber into an upper chamber and a lower chamber. A hammer is coupled to the mandrel between the upper and lower shoulders, i.e., the upper and lower anvils, of the housing.
When a portion of the drill string becomes stuck within the wellbore, either a tension or compression load is applied to the drill string and the hydraulic jar is then fired to deliver an impact blow intended to dislodge the stuck portion or component. For example, when a component becomes stuck below the hydraulic jar, a tension load may be applied to the drill string, causing the drill string and mandrel of the hydraulic jar to be lifted relative to housing of hydraulic jar and the remainder of the BHA, which remains fixed. As the mandrel, with a flow restrictor coupled thereto, translates upward, fluid pressure in upper chamber increases, and the hydraulic fluid begins to slowly flow from the upper chamber, through the restrictor, to the lower chamber. The increased fluid pressure of upper chamber provides resistance to the applied tension load, causing the drill string to stretch and store energy, an action typically referred to as cocking. When a predetermined tension load is reached, hydraulic jar is fired to deliver an impact blow. This is accomplished by releasing the tension load being applied to the drill string and allowing the stored energy of the stretched drill string to accelerate the mandrel rapidly upward within the housing until the hammer of the mandrel impacts the shoulder of the housing. The momentum of this impact is transferred through housing and other components of the BHA to dislodge the stuck component.
Drilling jars commonly use hydraulic release mechanisms, which can be of varying designs, but usually have a primary fluid passage, which is obstructed by a flow control device positioned in a restrictive bore. The valve configuration prevents the free movement of the hammer portion until such time as the flow control device moves out of the restrictive bore. In order to effect movement of the device, hydraulic fluid slowly bleeds through a fluid bypass creating a time delay until the valve clears the primary fluid passage allowing free movement of the hammer portion of the tool. When the restrictive bore is no longer obstructed by the flow control device, the hammer can telescope unobstructedly to create the desired impact.
Hydraulic jars may be bi-directional, meaning they are capable of delivering an impact blow in both the uphole and downhole directions. Alternatively, a hydraulic jar may be uni-directional, meaning it is designed for and is capable of delivering an impact blow in either the uphole or downhole direction, but not both. One problem with the prior art hydraulic drilling jars pertains to the arrangement of moving parts, which provide an orifice to restrict the flow of hydraulic fluid during the cocking action of the hydraulic jar. More specifically, it is difficult to jar in both directions using a single flow control valve, due to problems in getting the valve to center itself properly in the restriction. For that reason, most two way hydraulic jars use two hydraulic flow control valves, one of which is inverted. These bi-directional hydraulic jars have two separate triggering mechanisms, which artificially lengthen the tool and result in an unnecessarily complex valve device.
Other known types of hydraulic drilling jars rely on predetermined clearances between a large number of relatively moving parts to control the flow of hydraulic fluid between the upper and lower chambers. These moving parts often require tight manufacturing tolerances, which are subject to frequent failure due to contamination and malfunction due to wear. The problems associated with prior art drilling jars cannot be tolerated, particularly in jars that are employed in deep hole drilling, where the reliability and operating characteristics of a downhole tool must be given special consideration as maintenance and repairs are time consuming and costly.
Therefore, there is a need for a flow control valve or a flow control device that is mechanically uncomplicated, is capable of intermittent or continuous use without malfunction, is relatively compact, and has both uni-directional and bi-directional capability.
Furthermore, there is a need for a flow control valve or a flow control device capable of withstanding the pressure and temperature conditions of a deep well operating environment.
Lastly, there is a need for a hydraulic jar, which is easily serviced and repaired.
Embodiments usable within the scope of the present disclosure meet these needs.